1. Field of the Invention
The present invention relates to a flow velocity measuring device.
2. Description of Related Art
With electronic equipment such as personal computers cooled by a cooling fan, etc., reduction in air volume due to plugging of a filter incurs a decrease in cooling capacity to cause a fear that hindrance is generated in the function of the equipment, and so a flow velocity measuring device is used to monitor the wind velocity at all times so that when air volume is decreased, a fan is increased in revolutions and an alarm is given to a user. Conventionally, flow velocity measuring devices adopted in such use are constructed to arrange a sensor element in a flow passage to measure the flow velocity of an air. However, there is caused a problem that when conventional flow velocity measuring devices are used over a long term, dust and dirt in an air adhere to and accumulate on a sensor element to cause degradation in accuracy.
In order to solve the problem, JP-A-11-166720 discloses a device, in which a trap wall is provided in a flow passage and inertia of dust and dirt causes dust and dirt in an air flow to be caught by the trap wall, after which the air flow is conducted to a sensor element. However, the device disclosed in JP-A-11-166720 has a disadvantage that when the flow velocity of an air flow is low, dust and dirt are insufficient in inertia to be adequately separated, and involves a problem that when mounted horizontally, dust and dirt once caught by the trap wall positioned above the flow passage fall again in the air flow to be carried to the sensor element, so that the device is limited in an applicable range.